Marine Data Literacy 2.0

Providing instruction for managing, converting, analyzing and displaying oceanographic station data, marine meteorological data, GIS-compatible marine and coastal data or model simulations, and mapped remote sensing imagery





Home > 9. Operational/Synoptic > 9.14 > Cyclone Paths

9.14 Plotting Atlantic and Eastern Pacific Tropical Cyclone Paths in IDV: NHC

  • Exercise Title:  Plotting Atlantic and Eastern Pacific Tropical Cyclone Paths in IDV: National Hurricane Center (NHC)

  • Abstract:  In this exercise, which is quite elementary, you will learn how to obtain the latest expected trajectory information from the NHC for any of the identified storms in the Atlantic (or Pacific if you take that initial option).  The data can downloaded as a zipped set of three shapes:  A point shape, indicating the NHC's best guess about future locations of the storm at stated times; a line shape indicating the NHC's best guess about the storm's future path; and a polygon shape showing the NHC's best guess about the possible spread of storm locations (given the natural uncertainties) in days 1-3, and in days 4-5 from the present.  THIS LESSON IS PROVIDED FOR EDUCATIONAL PURPOSES ONLY.  NO ONE SHOULD ATTEMPT TO RELY ON THESE ANALYSIS PRODUCTS FOR NAVIGATION OR FOR ANY OPERATIONAL PURPOSES AT SEA.

  • Preliminary Reading (in OceanTeacher, unless otherwise indicated):

    • N/A

  • Required Software:

  • Other Resources: 

  • Author:  Murray Brown

  • Version:  September 2011

1.  Open the NHC website and read the general information about its activities and products.  Here you see the EASTERN PACIFIC version of the homepage.
2.  Here, we've clicked over to the ATLANTIC home page.
3.  Click on any available hurricane icon to see all these detailed products.  Hurricane Katia was present when this exercise was written.

If there is no current tropical cyclone, then this exercise isn't really useful.

4.  Click on DOWNLOAD GIS DATA and save the file to the folder DATA > OCEAN with the name which is a concatenation of the filename offered by NHC (al122011_5day_latest) and additional information to specify the exact time the file was obtained.  Note that Z-6 is the ISO specification for the Eastern Time Zone in the USA.
5.  Unzip the file in place.  You'll find these shapes:
  • al122011.034A_5day_pts.shp - Point shape, probably of sequential storm center locations
  • al122011.034A_5day_pgn.shp - Polygon shape, probably of storm location probabilities
  • al122011.034A_5day_lin.shp - Line shape, probably of expected storm center movement
  • al122011.034A_ww_wwlin.shp - Unknown object that doesn't plot in a standard GIS (Saga)
6.  In a "standard GIS" program, the first three of the above files plot as you see here.  The points are located 12 hours apart (for the first 5 locations) and 24 hours apart (for the final 3 locations).

The IDV documentation warns that point shapes don't work in IDV, without additional work, because it cannot handle one-dimensional points.  You can use the Saga tool MODULES > SHAPES/TOOLS > BUFFER SHAPE to create the small circles you see here.  We won't bother to do that during this lesson, but we'll confirm the point shape incompatibility issue in the panels below.

7.  Run IDV.
8.  Use DATA > DATA CHOOSER and navigate to the OCEAN data files.  Select DATA SOURCE TYPE: SHAPEFILE.  Then select the line, polygon and points SHP files.  Then click ADD SOURCE.
9.  In the FIELD SELECTOR, select the line shape object, and click CREATE DISPLAY.
10.  After clicking past a display settings window, you'll see this trajectory path for the storm for the next 5 days.
11.  In the same way, select the polygon shape, and click CREATE DISPLAY.
12.  Here are the combined shapes.  If you use a figure like this, be very careful to tell your readers/users that these are estimated locations, based on models, but the actual storm path could vear dramatically outside these cones.
13.  You can also try to visualize the point shape, in the same way, but nothing will appear.
14.  Now, you can clean up your graphic, by selecting the line shape in the right-hand list of objects.  Then select DISPLAYS > EDIT > PROPERTIES
15.  Edit the DISPLAY LABEL, as you see here.  Then click OK.

You should, in the same way, select the point shape object and delete its DISPLAY LABEL.  Then click OK.

Also select the polygon shape object and delete its DISPLAY LABEL.  Then click OK.


16.  Here you have a nice graphic with only one simple label, showing the probably path and the probability "cones.".
17.  A FINAL WORD OF CAUTION.  If you are not a certified meteorologist, then do not use the above methods and products to "publish" or circulate tropical storm analyses as if they were your own invention.  Make certain that everything you make here is clearly identified by you as having come from a specific other source, namely the National Hurricane Center of the USA.  And be very careful that you date your files and products so that older version can be scrapped and do not cause problems.  These are wonderful data products and software systems, but they can easily be abused and cause difficulties if you do not take care to educate users about their origins and purposes.